This invention relates generally to devices and systems for monitoring parameters of a selected fluid, particularly such as a process liquor used in manufacturing operations such as a paper mill or the like. More specifically, this invention relates to a sampling system for on-line monitoring of one or more fluid parameters of a process liquor, wherein the improved sampling system is designed for substantially continuous operation with a process liquor laden with a significant proportion of particulate material.
In many industrial operations, process fluids are used in the course of manufacture and/or treatment of industrial products. Such process fluids in form are often referred to as process liquors, frequently have a specific formulation which must be maintained within prescribed range limits for the industrial process to proceed in an efficient and economical manner. Accordingly, monitoring devices and systems are required to test one or more selected process liquor parameters on a periodic or continuous basis, thereby permitting appropriate remedial adjustment of the liquor formulation on an as-needed basis.
As one example, paper mills utilize a caustic process liquor to digest wood chips and/or other cellulosic material to produce pulp which is subsequently processed to form paper of different types and grades. The caustic process liquor is recovered from a digester unit for chemical recovery or regeneration and subsequent re-supply to the digester unit. The chemical recovery process involves a sequence of liquor treatment steps utilizing equipment such as boilers, dissolving tanks, clarifier tanks, etc., with frequent and/or continuous analysis of liquor parameters such as alkalinity being extremely desirable to insure that the process proceeds in an efficient, economical and safe manner. Efficient process performance can be of critical importance to insure a substantially constant supply of regenerated process liquor to the digester unit, in spite of flow surges and other process parameter variations which often occur.
In the context of paper mill liquor recovery processes, however, accurate monitoring of liquor parameters such as alkalinity is significantly hampered by substantial quantities of particulate and scale present in the process liquor. More particularly, monitoring devices such as pressure cell transmitter tubes have been installed into the process liquor to obtain density readings which can be correlated with alkalinity. Such pressure cell tubes unfortunately encounter frequent clogging with particulate and scaling. Other proposed monitoring devices having included radiation gauges and conductivity monitors which avoid tubing and related clogging problems, but otherwise encounter scale buildup resulting in inaccurate readings. Accordingly, to obtain accurate alkalinity measurements, it has been necessary to remove liquor samples from the process stream at periodic intervals for separate laboratory analysis by titration or optical refractometer techniques. Such separate analysis is unfortunately inadequate to permit rapid process cycle adjustment to accommodate potentially rapidly changing process conditions.
There exists, therefore, a significant need for improvements in fluid sampling systems, particularly with respect to providing on-line and substantially continuous liquor monitoring capability irrespective of the presence of substantial particulate quantities in process liquor. The present invention fulfills these needs and provides further related advantages.